1. Field of the Invention
The present invention relates to reactors used in the semiconductor manufacturing industry and, in particular, to a reactor for pulsed layer deposition of thin films in the fabrication of integrated circuits.
2. Description of Related Art
A primary goal of the semiconductor manufacturing industry is to reduce the size of integrated circuits in order to them to perform more operations in a shorter time. As integrated circuit device features become smaller, several technical difficulties are presented. One such problem is depositing conformal thin films in holes or trenches having a small diameter or a small width-to-depth ratio. One standard technique for depositing such thin films has been chemical vapor deposition (CVD), which works well for feature sizes on the order of 120 nm and smaller. However, CVD may not be extendable to high aspect ratio features at these dimensions. Pulsed layer deposition (PLD) has been seen as a likely replacement for film deposition and holes below 120 nm in width and for the high aspect ratio features.
PLD is useful for depositing thin films having two components. The process generally consists of four steps, which may be repeated to produce films of desired thickness. The steps are normally conducted in a reactor with a controlled environment. The first step consists of saturating a surface with the first precursor or reactant needed to create the film, followed by removing the excess byproducts of the first reaction and any unreacted precursor from the reactor. The next step consists of saturating the surface with a second precursor or reactant in order to form the desired film. The last step is to remove unwanted excess byproducts from the third step and any unreacted precursor.
The precursor exposure steps of PLD are said to be self-limiting, that is, the amount of material deposited on the surface stops depositing after a relatively short period of time. However, in order for the deposition reactions of steps one and three to go to completion, the surface must receive a high exposure of the precursor. This is achieved if the precursor is allowed to remain for a long period above the surface or if the concentration of the precursor above the wafer is high. Provided the precursor exposures are high and the purging performed during the second and third steps are sufficient, there results a thin film consisting of the reaction product of the two components. The purging steps are sufficient if concentrations of the un-reacted precursors and reaction byproducts are low enough to minimize or eliminate one precursor or its byproducts from contacting, and possibly reacting with, the second precursor or its byproducts.
In addition to the steps outlined above, there are additional practical requirements. First, each step should be as short as possible to fulfill the requirement that the thin film be formed as fast as possible to make the entire process commercially viable for ultra large scale integration (ULSI) of the circuits. Second, the smallest possible amount of precursor should be used because precursor costs must be minimized to make the process commercially viable, and un-reacted precursor and byproducts must be minimized to reduce the need for abatement of environmentally harmful substances. Accordingly, the requirements for a rapid process and use of minimum amount of precursor, coupled with the requirements of high exposure and sufficient purging, necessitate trade offs to be made in the PLD process.